This invention relates generally to systems which optically scan the human eye and, more particularly, to systems that image, or project an image to the eye.
There is considerable interest in entertainment and/or educational systems that provide a more realistic experience to a user and that do not require the substantial hardware and software typically employed by a full-field video projection system. For example, modern xe2x80x9cvirtual realityxe2x80x9d apparatus typically include video and audio signal generators that provide signals to a headset in accordance with instructions received from a controller. The headset projects a near field image inches away from the viewer, typically completely occupying the field of the vision of the viewer""s eyes. Most such virtual reality systems alter the view presented to the viewer in response to the position of the viewer""s head, as sensed by the headset, such that the view changes in much the same manner that a far field image received by the human eye would vary.
While these virtual reality systems overcome the disadvantages of large projection and reflective screens found in conventional projection systems, the cumbersome headset is still a limitation. Moreover, the optical systems of the virtual reality apparatus typically still form an image on a screen, albeit a smaller screen, so as to provide the image to viewer""s eyes.
It is possible present an image to a viewer by scanning the viewer""s eye or eyes with a modulated beam of light. Such systems directly present the image to the viewer""s retinas, thereby advantageously obviating the need for either far field or near field projection screens. Apparatus and methods for scanning the eye are known and used in systems for examining particular attributes of both the interior and exterior of the human eye.
For example, systems are known for scanning the iris of the eye and typically, include an imager which obtains a video image of the iris of each person and compares the image with known patterns stored in the system memory. The human iris is essentially unique for each individual and, unlike other forms of direct personal identification such as fingerprints, does not lend itself to alteration or misinterpretation. Iris patterns can thus be used as a basis for identification aid in controlling, for example, access to secured facilities or to an automated transaction machine (ATM). Examples of these systems are found in U.S. Pat. Nos. 5,572,596 and 5,291,560, both of which are herein incorporated by reference.
Other known systems examine retinal vasculature patterns by scanning a fixated eye with a light source arranged in a selected pattern and detecting that portion of the pattern which is reflected off of the retina. The reflected light source pattern is analyzed for each intercept of the light with a blood vessel. The intercept pattern is stored for future recall and comparison with subsequently obtained pattern(s). Identification systems can use such comparisons since, like the iris, a retinal vasculature pattern is unique and constant. The analysis is performed by one of a number of algorithms which identifies a match between the scanned and stored retinal vasculature pattern. An example of this type of device is shown in U.S. Pat. No. 4,109,237, herein incorporated by reference.
With the foregoing systems, the eye is carefully illuminated and either the retina of iris is scanned to record a detailed image. The scanning apparatus is quite precise, but is nevertheless not free of large bulky equipment and lossy optical components.
Regarding scanning to produce an image, techniques for creating virtual displays via retinal scanning of laser beams have been developed by, inter alia, the Human Interface Laboratory at the University of Washington, and commercialized via Microvision. The technology of these systems involves the modulation of laser beams directed onto the retina of the eye. By modulating the intensity as well as the vertical and horizontal sweep of a laser beam at high speed, a video-like image can be formed onto the retina. A tiny xe2x80x9cmicro machinexe2x80x9d mirror deflects the laser beam in the horizontal and vertical axes simultaneously. As this technology develops, ever greater resolution and bandwidth will be required to deliver images which are similar to VGA, SVGA, XVGA, NTSC, HDTV etc., thus requiring the micro mirror device to be successfully modulated at extremely high frequencies.
Scanning systems such as those described above typically involve modulating a physically moving mirror in the horizontal axis at one frequency while modulating it at the same time in the vertical axis, often so as to replicate the conventional raster sweep of an electron beam of a cathode ray tube, and thus requiring the mirror or mirrors to oscillate in an unnatural way. This can require exercising considerable dynamic control and overcoming significant magnetic energy. At the same time, use of the raster scan to produce high resolution imagery over the entire field of view can require a large bandwidth.
Thus, although existing systems for scanning the eye, such as the examination and presentation systems described above, are impressive, improvements can be made. Accordingly, it an object of the present invention to overcome one or more of the aforementioned disadvantages of the prior art, such by providing methods and apparatus for the improved scanning of the eye, such as for the presentation of images to, and/or the examination of, the eye
In one aspect of the present invention, an apparatus directly projects an image onto a retina. The apparatus includes an optical source for generating a light beam to be focused on a retina. A projection device sweeps the light beam along the retina in an ellipsoidal pattern such that a higher spatial concentration of light pixels impinge a selected portion of the retina than a peripheral portion thereof. A controller is coupled to the optical source and the projection device for modulating the light beam such that a higher temporal concentration of light pixels impinge a central portion of the retina than a peripheral portion thereof.
In another aspect of the present invention, a method is provided for directly projecting an image onto a retina. A light beam is generated and swept along a retina in an ellipsoidal pattern such that a higher concentration of light pixels impinge a central portion of the retina than a peripheral portion thereof. The light beam is modulated such that a higher temporal concentration of light pixels impinge a central portion of the retina than a peripheral portion thereof.
In one aspect, the invention a system of the foregoing type which is characterized by a weighted projection function such that the more sensitive areas of the human retina selectively receive the projected image.
In another aspect, the present invention can provide a system of the foregoing type in which the image is projected into a selected zone of the human retina, reducing overall system bandwidth requirements.
In yet another aspect, the present invention includes an image projection apparatus of the foregoing type which generates pixels in an ellipsoidal sweeps that rotate around a central axis.